Nucleophilic additions organic radical ions

The number of solvents that have been used in SrnI reactions is somewhat limited in scope, but this causes no practical difficulties. Characteristics that are required of a solvent for use in SrnI reactions are that it should dissolve both the organic substrate and the ionic alkali metal salt (M+Nu ), not have hydrogen atoms that can be readily abstracted by aryl radicals (c/. equation 13), not have protons which can be ionized by the bases (e.g. Nth- or Bu O" ions), or the basic nucleophiles (Nu ) and radical ions (RX -or RNu- ) involved in the reaction, and not undergo electron transfer reactions with the various intermediates in the reaction. In addition to these characteristics, the solvent should not absorb significantly in the wavelength range normally used in photostimulated processes (300-400 nm), should not react with solvated electrons and/or alkali metals in reactions stimulated by these species, and should not undergo reduction at the potentials employed in electrochemically promoted reactions, but should be sufficiently polar to facilitate electron transfer processes. 

The synthesis of complex ring-systems is still a challenge in organic chemistry. With the exception of cycloadditions, the ring-building key step is always an intramolecular bond formation. In PET-initiated reactions, this step can be an addition (or recombination) reaction of a radical or radical ion or a nucleophilic... 

In addition to simple electron transfers in which no chemical bond is either broken or formed, numerous organic reactions, previously formulated by movements of electron pairs, are now understood as processes in which an initial electron transfer from a nucleophile (reductant) to an electrophile (oxidant) produces a radical ion pair, which leads to the final products via the follow-up steps involving cleavage and formation of chemical bonds [11-23], The follow-up steps are usually sufficiendy rapid to render the initial electron transfer the rate-determining step in an overall irreversible transformation [24], In such a case, the overall reactivity is determined by the initial electron-transfer step, which can also be well designed based on the redox potentials and the reorganization energies of a nucleophile (reductant) and an electrophile (oxidant). 

Nucleophilic addition reaction is one of the most common reaction pathway available to organic cation radicals. Therefore, as expected alkene radical cations are also attacked by a variety of nucleophiles to give anti-Markonikov addition products. In this context the pioneering work of Arnold [60, 61] may be cited here by illustrating (Scheme 12) the addition of alcohol or cyanide ion... 

Aromatic compounds have been used as electron acceptors and electron donors in PET-processes since the early beginnings of photochemistry. Chapter 4 of this volume is devoted to this still fascinating area mainly from the synthetic point of view. Special emphasis is given to recombination reactions of radical ions, electrophilic, nucleophilic and radicalic additions. The following article extends this topic to recent advances of PET in organic... 

This review article deals with addition and cycloaddition reactions of organic compounds via photoinduced electron transfer. Various reactive species such as exdplex, triplex, radical ion pair and free radical ions are generated via photoinduced electron transfer reactions. These reactive species have their characteristic reactivities and discrimination among these species provides selective photoreactions. The solvent and salt effects and also the effects of electron transfer sensitizers on photoinduced electron transfer reactions can be applied to the selective generation of the reactive species. Examples and mechanistic features of photoaddition and photocycloaddition reactions that proceed via the following steps are given reactions of radical cations with nucleophiles reactions of radical anions with electrophiles reactions of radical cations and radical anions with neutral radicals radical-radical coupling reactions addition and cycloaddition reactions via triplexes three-component addition reactions. 

This review article deals primarily with addition reactions of nucleophiles, electrophiles, and neutral radicals to photochemically generated radical ions of organic compounds and some organometallic compounds. Photocyclodimerizations of electron-rich alkenes, photo-Diels-Alder reactions between alkenes and alkadienes via dimer or heterodimer radical cations, and photocycloadditions via triplexes are also included. 

Nucleophilic addition to organic radical cations is one of the most common available reaction pathways. Usually, alkene radical cations give anti-Mark-onikov addition products with a variety of nucleophiles. In this context, the pioneering work of Arnold et al. [132,133] for the addition of alcohol or cyanide ion to conjugated alkenes may be cited. 

The distannane mediated organic radical addition to A -acyliminium ions [13], and the benzylic radical addition to A/ -acyliminium ions which proceeds via radical/cation/radical cation chain mechanism [14] show that the cation pool can be utilized as good nucleophilic radical acceptors because of their strong electrophilic character. Iterative molecular assembly based on the cation pool method lead to the efficient formation of dendritic molecules [15]. The manipulation of the cation pool in the microflow system realized an efficient... 

One important feature of ion-radical organic reactions consists of a possibility to nudge them by the introduction of active reactants. Thus, in the reaction of an electron acceptor with electron donors (nucleophiles), the addition of a tiny amount of a nucleophile, which is more active at initiation of the one-electron transfer allows the less reactive nucleophile to start its own chain propagation. A method called entrainment is widely used in chemical practice as a recent example (see Schmidt et al. 2007). 

In addition, the hydrated electron acts as a nucleophile, especially with organic molecules that contain halogen atoms (Eq. 6-16). This reaction results in rapid elimination of a halide ion from the initially formed negatively charged organic species. The reaction of Eq. 6-16 is of special interest for the degradation of per-halogenated saturated hydrocarbons that are usually not affected by hydroxyl radicals (Sun et al, 2000). 

Organic fluorine compounds and methods for their preparation are the central topic of the next four procedures. Much of the synthetic versatility of methyl phenyl sulfone is embodied in FLUOROMETHYL PHENYL SULFONE and the fluoro Pummerer reaction of methyl phenyl sulfoxide with DAST is a key step in its preparation. The utility of this fluoromethyl sulfone in the preparation of fluoroalkenes Is demonstrated in a companion procedure for Z-[2-(FLUOROMETHYLENE) CYCLOHEXYL]BENZENE, a procedure with several prominent stereoselective features. Geminal difluoroalkenes are featured in the following procedure. (3,3 DIFLUOROALLYL)TRIMETHYLSILANE is prepared by a method in which the radical addition of dibromodifluoromethane to alkenes and the selective reduction of a-bromoalkylsilanes are key steps. A procedure for nucleophilic introduction of the trifluoromethyl group completes this set. The key reagent, (TRIFLUOROMETHYL)-TRIMETHYLSILANE is obtained by reductive coupling of TMS chloride and bromotrifluoromethane. Liberation of a CF3- equivalent with fluoride ion in the presence of cyclohexanone affords 1-TRIFLUOROMETHYL-1-CYCLOHEXANOL. 

The employment of suitable organic solvents, such as acetonitrile and acetic acid, with oxidation-resistant supporting electrolytes permits the anodic formation of reactive radical cations from many organic materials. Most aromatic compounds and olefins, as well as those alkanes which have particularly weak C—H bonds, are oxidised in acetonitrile containing fluoroborate or hexafluorophosphate electro-lytes. °" 2 Some aromatic radical cations can be further oxidised to dications within the available potential range. Radical cations in general either deprotonate or attack nucleophiles present in the medium reactions with pyridine, methanol, water, cyanide ion, acetate ion or acetonitrile itself produce addition or substitution products. The complete reactions involve a second electron transfer and coupled chemical... 

In reactions with organic molecules e q reacts as nucleophilic reagent it attacks molecules with low-lying molecular orbital, like aromatic hydrocarbons, conjugated olefinic molecules, carboxyl compounds, and halogenated hydrocarbons (Swallow 1982 Buxton 1982, 1987 Buxton et al. 1988). In the latter case, addition is usually followed by halide ion elimination, so the reaction can be considered as a dissociative electron capture. For instance, the reaction with chlorobenzene yields phenyl radical and chloride ion... 

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